1. Field of the Invention
The present invention relates to a ceramic-metal composite unit or assembly of the kind wherein a ceramic member and metallic member are joined together with a mechanical joining means.
2. Disclosure Information
For joining a ceramic member and a metallic member together, a chemical joining means such as brazing and a mechanical joining means such as fits are known. The fits for this end are press fit, shrinkage fit, expansion fit, etc.
Production of a ceramic-metal composite assembly by the shrinkage fit or expansion fit requires a large-scaled apparatus and therefore has a problem of a high cost. Another problem of the composite assembly by the shrinkage fit or expansion fit is that large residual stresses are caused after assembling. A further problem of the composite assembly by the shrinkage fit is that the shrinkage fit causes metallographic structure transformation and cannot attain such a sufficiently large interference as is attained by the expansion fit.
The composite assembly produced by press fit or forced fit can attain a larger interference as compared with that produced by shrinkage fit or expansion fit but is encountered by a problem that abrasion is caused between the ceramic member and the metallic member, that is, the metallic member is caused to partially adhere to the ceramic member on press fit and thus have a ragged joining surface. Such abrasion at the joining portions is causative of breakage of the ceramic member of itself due to stress concentration resulting from spotty contact, decrease of the joining strength and vibrations when the assembly is used as a rotor.
A ceramic-metal composite assembly in which a ceramic member and metallic member are joined together by press fit or forced fit, is disclosed by Japanese Patent Provisional Publication No. 62-4528. The composite assembly is constructed such that the difference between the outer diameter of the projection of the ceramic member and the inner diameter of the depression of the metallic member when the projection of the ceramic member is extracted from the depression or through hole of the metallic member is not less than 0.2% of the outer diameter of the projection of the ceramic member.
While the composite assembly disclosed by the above publication document may attain a sufficiently large interference, it is still encountered by a problem resulting from the above described abrasion of the ceramic member and therefore has a possibility of breakage of the ceramic member of itself due to stress concentration, decrease of the joint strength and vibrations when the assembly is used as a rotor.